Attempting a cambelt change, I've undone the crank pulley bolt, turned it 3 or 4 revolutions but it feels like the thread's picked up. It won't re-tighten without excessive force either. Letting some WD40 soak in while I ponder.
Feels like it will snap before it comes out, so now I have a dilema - I could:

1. Carry on regardless, but if it snaps or strips the thread so it won't go back in that's probably game over for a car I rather like.

2. Attempt to re-tighten it, outcome probably as above.

3. Try to slot some washers to fill the gap twixt bolt head and the pulley so it only needs say one turn to lock the pulley in place. Might work as a short term fix, but what then?

Guess I don't absolutely need to do the timing belt this minute, but it's 94k / 3 years since I did it last and I'm hoping to prove/eliminate the water pump as the cause of my minor fluid loss.

Lord knows! I reckon jasper's your best bet. It's another one of them "whatever I do will be wrong" situations but, without resolving it one way or t'other, you'll be driving a car that could go pop! at any moment. I reckon I'd try rocking the bolt back and forth, try and work it out bit by bit and hope it's not damaged the crank too much.

without resolving it one way or t'other, you'll be driving a car that could go pop! at any moment

Worse than that, the crank pulley's loose so it ain't a goin nowhere.

---or wasn't. I took the semi cowardly way out and tightened it back up v e r y c a r e f u l l y.
The last turn or so was almost free, so I naturally tried undoing it again and again and then resisted adding to 40-odd years of not quite learning when to give up. So it's done up for now and therefore derivable, while I work on Plan B.

In my experience once a thread has picked up it's game over,it's a weird phenomena no amount of force will undo it but it will do up again,not really a feesable option but the only way i can see to save the threads in the crank is to drill the bolt out.

Don't fancy my chances of drilling the bolt accurately enough to save the thread in the crank - not the easiest place to ensure you get it dead centre and the drill constantly on the right axis, but may have to try it if all else fails.

Impact wrench may be an option, half the problem is the inability to prevent the engine turning with a wheel off. I shall think about an effective way of locking it.

Eric,
When it was last done, did it have a new bolt installed ?
The reason I ask is I've done mine twice now each time with a new bolt from the main steelers.
These bolts come with locking paste already on them, this can make them feel as though there picking up
as you wind them out.
I have always done it John's way with the breaker bar on the floor & wind it out on the starter,
The last time I had already disconnected the ecu, so just kept it on the starter until if fell out

As long as you don't, didn't re-use the old pulley bolt you should be golden

..but then I changed the crank pulley last year and re-used the same one, since only normally get a new one with a belt kit.
came out easily last time, went back in easily and was torqued up correctly.

Didn't risk forcing it yesterday, I was having to use the breaker bar to turn it so the more it unscrewed the greater the sideways force/risk of snapping it. Going to have another go probably with a battery impact wrench so I can ease it back and forth without any load in the wrong axis.
Also plan to gather a set of cobalt drills, taps etc
ServiceBox describes the Crankshaft Pulley Screw as M14x150-70, which I suspect means a 70mm long M14x1.5 part-threaded screw, (M14 fine is 1.5mm pitch). A bit like this:

If it does shear off, I'm hoping it might leave at least a little thread protruding from the crank. This would allow me to fit a s/s capped nut with a pre-drilled pilot hole spot-on centre, so even I can start drilling in the right place for once. We'll see.

If it should break off, even if its flush you could weld an nut onto the stub through the hole, not only will that give you something to grip but the heating will expand the hole more than the bolt which also helps.

I don't know if you have already sorted this problem, I've been away so didn't see the post.

My solution to this problem is this...
If you have got the bolt moving carry on with the WD40 into the threads and moving the bolt in and out gradually.
I usually use the starter motor trick but that might not be a good idea in the circumstances, but if you are brave enough....

If the bolt was similar to the one in the pic with thread lock on it's possible that it is jamming on the thread lock (99% of the time that is the case)...applying heat to the bolt would soften the thread lock then hitting the end of the bolt will free it up.
To lock the engine there are crank locking tools which slide into the teeth of the flywheel and then bolt into a bolt hole around the gearbox casing which is exposed where a tin plate might be....they aren't expensive...in fact the Peugeot locking kit has one of these in it.

If all else fails and the bolt breaks there is a foolproof method of drilling straight into the centre of the bolt...it requires a bit of engineering but it works....

Make up a round piece of metal that fits snugly into the bolt hole with a small diameter hole for a pilot then drill a pilot hole.
Gradually increase the hole with bigger drill bits until you get to the size of the bolt or intervene with an easy out somewhere in the process.
Hopefully you can get a tap in and clean up the thread.
If you can get hold of some left handed drill bits then the process could be easier if you think about it.

Not resolved as yet, waiting for a window when I can afford to have it off the road for a few days if necessary. There's no compelling rush to get it done, I'm hoping to confirm or eliminate the water pump as the cause of the minor coolant loss I've had on & off for a few months.

That's a good suggestion for getting the drill on centre, I may well try that. I'll look for a crank locking gubbins too.
Many thanks for your help, always appreciated.

I got it sorted yesterday.
Invested in a new crank pulley bolt kit and a Laser 3203 locking device:
Which set me back about £20 all told.
I applied the locking gadget after removing a small section of cover just below the starter - it didn't really fit in the sense there was no way to bolt it in place, but when pushed into the teeth, the flywheel would only move about half a tooth either way. (Didn't notice at the time, but there's similar cover on t'other side just by the driveshaft, maybe that's the right one)?
Anyway this was good enough for me to ease the bolt out. Had intended to borrow an electric torque wrench so as to avoid any side load on the bolt, but in the end settled for next best approach - 2 x 300mm extension bars and a ratchet. Car was up fairly high on axle stands, so this arrangement allowed me to stand upright facing the wing and keep everything nice and straight/perpendicular.
For some reason I can't fathom, the bolt turned easily while rotating the ratchet in a narrow arc either side of horizontal, but tightened up dramatically in any other position. Keeping to this technique and working it back and forwards a little, the bolt unscrewed fully in about 10 minutes.
No discernible damage to the tread in the crankshaft and very little to the bolt, a few tiny chips in the thread and oodles of loctite. Scrubbed it all off with a brass brush, dab of oil and it screwed back in all the way by hand.
Carried out a standard timing belt/idler/tensioner swap. Absolutely no sign of leakage or play in the water pump, so I left it alone.
Said to myself, "that'll be the last timing belt I put on this car", just like I did last time.
(At nearly 15 years old and 221k miles, it's probably true this time).
Still no wiser about the 'leak' if leak it be - I haven't topped it up since August - but at least the need for a cambelt change will stop colouring my thinking.
After starting it 3 or 4 times to check everything, the battery was flat when I wanted to use it.
Oh well, this one's done 6 years so no real surprise there.

That just leaves me a rear drop link or two and a noisy bearing. (Which probably means 2 hubs and another rear brake overhaul).
I know the backplates are like swiss cheese, so this isn't going to be easy or cheap. If it wasn't for the backplate issue I'd get someone else to do it
Having said all that, driving it again after a few days of borrowing other elderly cars reminds me why I've stuck with it so long. Still nowt out there I'd want to swap it for.

Glad you got it sorted
I thought you would do it with the locking tool....the Peugeot one has a 90 degree bracket on it for bolting to one of the tin plate mountings if I remember.
I've had quite a few like this which usually undo by fitting a bar and socket to the bolt and held by the driveshaft...turning the key until the bolt comes out far enough for wd40 to go into the threads...the noise is quite unnerving as it rips through the locktight stuff.
Some big penny washers will help with mounting the shoes, or some metal shaped and drilled to fit around the rotten bits.

Well done young man! I'll bet that's a weight off your mind. So it was just the loctite doing that? I suppose that's what it's for but it's not really meant to give you a nightmare. I suppose the sticky bits where were some of the loctite was on the bolt, some of it in the crank, and that was just forcing one over the other.

I've got a saved search on ebay for backplates and I've seen prices fall, but they've only gone from solid gold to gold-plated It really depends if you're likely to keep it forever. As Jasper says, big washers and replace pins with small nuts and bolts. I'd probably take my mig to them but that would probably be overkill, it really doesn't need to be anything special.